![]() My first attempt at integrating the piece-table into Neatpad went quite smoothly. Usually that’s where the tricky part comes in, but fortunately we now have the piece-chain sequence class which will enable us to make edits to the underlying document each time a character is received. Regardless of how the text is entered, all we need to do is receive each WM_CHAR as it is sent to the TextView and process it accordingly. However it is very unlikely that a user will manually enter two surrogate values separately - more than likely they will be using an Input Method Editor, and it will be the IME that breaks their keyboard input into UTF-16 units. > 0xFFFF in value) will be sent as two separate messages, one for each surrogate character. As long as we compile with the UNICODE macro defined we will receive UTF-16 characters. We don’t need to do anything special to receive Unicode input. ![]() The code below shows the standard method of handling character-input in a Win32 program:Ĭase WM_CHAR : return OnChar ( wParam, lParam ) Although we will ignore these additional input-messages, we will not be losing any functionality by simply handling WM_CHAR at this point. Likewise the WM_IME_CHAR message is only sent under special circumstances. I suspect that this is a message that is sent by other applications (such as IME’s) rather than the OS itself. ![]() Supposedly the WM_UNICHAR message sends UTF-32 characters rather than the 16bit WCHARs - however I have never seen WM_UNICHAR being sent to a program, even on a XP machine. The other messages look interesting but are not really necessary. The Windows Input Method Editor will be the subject of a future tutorial. Even complex scripts will be handled seemlessly because keyboard input for these languages is usually associated with an Input Method Editor (IME) - which will translate any ‘complex’ key-strokes into the appropriate stream of UTF-16 characters, without any extra work on our part. This is perfect for us, because Neatpad is already an UTF-16 (wide-character) application. For any UNICODE application, the WM_CHAR message sends a single UTF-16 character value instead of a plain ANSI character. We already looked at keyboard navigation in Part 16 - Keyboard Navigation, in which we discussed caret movement within a Unicode document, and we briefly looked at the various Win32 character-input messages that a program can encounter when receiving keyboard input:Įven though the WM_CHAR message has been around since the first versions of Windows, it is still the most appropriate way for a Win32 application to receive character input. The purpose of this tutorial is therefore to document the modifications required by Neatpad to support the piece-table editing model. The sequence class was presented which encapsulates the piece-table and these basic editing operations within a single C++ object. Unlimited undo and redo are also supported. The last tutorial saw the implementation of a piece-table data structure which implements three basic edit operations: insert, erase, and replace. The Uniscribe API will again be used to aid us in this area.Ĭharacter input (of any kind) is not possible without some form of data-structure to manage and represent any alterations to the document. Modifications to a Unicode text-file require careful coding to ensure that character cluster-boundaries are preserved and that no invalid sequences are inadvertantly introduced into the document. The main difficulties are the Unicode ‘combining sequences’ - where multiple code-points are combined to form a single selectable ‘character cluster’. Characters that differ from ISO-8859-1 is marked by light blue color.Unicode character input presents some unique problems for text-editors - issues that did not have to be considered when the first ASCII editors were written. Is a superset of ISO 8859-1, also called ISO Latin-1, in terms of printable characters, but differs from the IANA's ISO-8859-1 by using displayableĬharacters rather than control characters in the 128 to 159 range. The table below is according to Windows-1252 (CP-1252) which There are several different variations of the 8-bit ASCII table. Character 127 represents the command DEL. You will find almost every character on your keyboard. The first 32 characters in the ASCII-table are unprintable control codes and are used to control peripherals such as printers.ĪSCII printable characters (character code 32-127)Ĭodes 32-127 are common for all the different variations of the ASCII table, they are called printable characters, represent letters, digits, punctuation marks, and a few miscellaneous symbols. ASCII control characters (character code 0-31)
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